1. Field of the Invention
The present invention relates to a sewing machine with a built-in driving motor, and more particularly to a sewing machine having an arm in which the driving motor is located.
2. Description of Related Art
Conventionally, a frame of a sewing machine includes a horizontally extending bed, a pedestal standing on the bed at one end portion thereof, and a cantilever arm having one end supported by the pedestal and having the other end extending parallel to the bed. A motor for driving the sewing machine is an AC servo motor or the like, and it is normally mounted under a table on which the sewing machine is mounted.
A driving force of the motor is transmitted through a belt and a pulley provided outside the arm to a main shaft provided in the arm. A needle bar and a thread take-up lever are driven by the rotation of the main shaft. Further, the driving force of the motor transmitted to the main shaft is transmitted through a cam, a vertical shaft, etc. to a bottom shaft provided in the bed. A feed dog and a loop taker are driven by the rotation of the bottom shaft.
U.S. Pat. No. 4,807,548 discloses a sewing machine having a driving motor located in a central portion of an arm. This sewing machine is very compact since the motor is located in the arm.
However, as the central portion of the arm is protruded in the air and is not supported at a lower portion thereof, the location of the motor, which is relatively heavy in the central portion of the arm, causes weight unbalance of the sewing machine. Accordingly, vibration is increased when the sewing machine is driven. Furthermore, the strength of the arm and the pedestal must be made large in order to support the motor, thus causing an increase in weight of the sewing machine. Further, the arm is formed from a cylindrical casting. Therefore, when mounting the motor in the central portion of the arm, it is necessary to deeply insert the motor into the arm and fix the motor to the arm using a long screw. Accordingly, the assembly and disassembly operation of the motor with respect to the arm when maintenance or the like is required becomes very troublesome.